The prescription medications came onto the market before a law that required makers to prove their effectiveness. Many of the unapproved drugs, however, are already discontinued, a pharmacist says.

Reporting from Washington — The Food and Drug Administration on Wednesday ordered the makers of about 500 unapproved prescription cough and cold medicines to get them off the market because they have not been proven safe and effective.

The drugs have been linked to a few relatively minor problems, such as drowsiness and irritability, but the FDA is concerned that medical problems associated them may be significantly underreported.

"We have some specific safety concerns with some of them," Deb Autor, head of compliance in the FDA's drug office, said in a telephone news conference.

Some of the targeted drugs are labeled as suitable for infants and children but contain ingredients covered by a 2008 FDA advisory that warned against using over-the-counter medications in children under age 2.

Others are billed as timed-release products. Such medications are difficult to manufacture and, if quality controls are inadequate, some may release drugs too slowly, too quickly or not at all, Autor said.

The FDA also moved against several unapproved products that contain possibly dangerous combinations of drugs, such as two antihistamines, which can cause oversedation.

None of the drugs is a household name, though Autor listed Cardec, Lodrane 24D, Organidin and Pediahist as brands consumers may have encountered.

In addition, none of the drugs fills a unique niche. "There are multiple other [approved] products available," Autor said.

Many of the drugs came on the market before a 1962 law that required makers to prove their effectiveness. It's not clear how much of a public health threat they may pose.

A pharmacist who reviewed the FDA's list of unapproved cough and cold drugs said many of them are already off the market. "A lot of these medications have been discontinued. They're no longer available," said Sophia DeMonte, speaking on behalf of the American Pharmacists Assn.

Wednesday's announcement does not affect over-the-counter preparations, which are widely used to treat cough and cold symptoms.